The research proposed in this grant will be directed toward understanding the role of one of the subunits, the alpha-subunit, which composes the multi-enzyme complex, tryptophan synthetase (bacterial). Utilizing both chemically and mutationally altered alpha-subunits, structure-function relationships which are concerned with the catalytic activity of the protein alone and in combination with the other subunit, the beta 2-subunit, will be explored. Additional information regarding the specific protein-protein interactions involved in the formation of the active, fully constituted multi-enzyme complex will be sought.